1. Field of the Invention
The present invention relates to a lithographic projection apparatus.
2. Description of the Related Art
The term xe2x80x9cpatterning devicexe2x80x9d as here employed should be broadly interpreted as referring to device that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate. The term xe2x80x9clight valvexe2x80x9d can also be used in this context. Generally, the pattern will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit or other device (see below). An example of such a patterning device is a mask. The concept of a mask is well known in lithography, and it includes mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. Placement of such a mask in the radiation beam causes selective transmission (in the case of a transmissive mask) or reflection (in the case of a reflective mask) of the radiation impinging on the mask, according to the pattern on the mask. In the case of a mask, the support structure will generally be a mask table, which ensures that the mask can be held at a desired position in the incoming radiation beam, and that it can be moved relative to the beam if so desired.
Another example of a pattering device is a programmable mirror array. One example of such an array is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that, for example, addressed areas of the reflective surface reflect incident light as diffracted light, whereas unaddressed areas reflect incident light as undiffracted light. Using an appropriate filter, the undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light behind. In this manner, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. An alternative embodiment of a programmable mirror array employs a matrix arrangement of tiny mirrors, each of which can be individually tilted about an axis by applying a suitable localized electric field, or by employing piezoelectric actuators. Once again, the mirrors are matrix-addressable, such that addressed mirrors will reflect an incoming radiation beam in a different direction to unaddressed mirrors. In this manner, the reflected beam is patterned according to the addressing pattern of the matrix-addressable mirrors. The required matrix addressing can be performed using suitable electronics. In both of the situations described hereabove, the patterning device can comprise one or more programmable mirror arrays. More information on mirror arrays as here referred to can be seen, for example, from U.S. Pat. Nos. 5,296,891 and 5,523,193, and PCT patent applications WO 98/38597 and WO 98/33096, incorporated herein by reference. In the case of a programmable mirror array, the support structure may be embodied as a frame or table, for example, which may be fixed or movable as required.
Another example of a pattering device is a programmable LCD array. An example of such a construction is given in U.S. Pat. No. 5,229,872, incorporated herein by reference. As above, the support structure in this case may be embodied as a frame or table, for example, which may be fixed or movable as required.
For purposes of simplicity, the rest of this text may, at certain locations, specifically direct itself to examples involving a mask and mask table. However, the general principles discussed in such instances should be seen in the broader context of the patterning device as hereabove set forth.
Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the patterning device may generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising one or more dies) on a substrate (silicon wafer) that has been coated with a layer of radiation-sensitive material (resist). In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the projection system, one at a time. In current apparatus, employing patterning by a mask on a mask table, a distinction can be made between two different types of machine. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion at once. Such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatus, commonly referred to as a step-and-scan apparatus, each target portion is irradiated by progressively scanning the mask pattern under the projection beam in a given reference direction (the xe2x80x9cscanningxe2x80x9d direction) while synchronously scanning the substrate table parallel or anti-parallel to this direction. Since, in general, the projection system will have a magnification factor M (generally  less than 1), the speed V at which the substrate table is scanned will be a factor M times that at which the mask table is scanned. More information with regard to lithographic devices as here described can be seen, for example, from U.S. Pat. No. 6,046,792, incorporated herein by reference.
In a known manufacturing process using a lithographic projection apparatus, a pattern (e.g. in a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist). Prior to this imaging, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the imaged features. This array of procedures is used as a basis to pattern an individual layer of a device, e.g. an IC. Such a patterned layer may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemo-mechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. Eventually, an array of devices will be present on the substrate (wafer). These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc. Further information regarding such processes can be obtained, for example, from the book xe2x80x9cMicrochip Fabrication: A Practical Guide to Semiconductor Processingxe2x80x9d, Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN 0-07-067250-4.
For the sake of simplicity, the projection system may hereinafter be referred to as the xe2x80x9clens.xe2x80x9d However, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics, and catadioptric systems, for example. The radiation system may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a xe2x80x9clensxe2x80x9d. Further, the lithographic apparatus may be of a type having two or more substrate tables (and/or two or more mask tables). In such xe2x80x9cmultiple stagexe2x80x9d devices the additional tables may be used in parallel or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures. Dual stage lithographic apparatus are described, for example, in U.S. Pat. No. 5,969,441 and WO 98/40791, incorporated herein by reference.
Within lithographic apparatus supports are required that provide a permanent force to oppose gravity. For instance quasi-static supports are required to support an isolated reference, or metrology, frame (which supports the projection system and various sensor devices) and isolate it from external vibrations. Dynamic supports are, for instance, required to support a short-stroke module for a substrate or patterning device on a long-stroke module. In such dynamic supports a static force component is provided to support the weight of the short-stroke module and a dynamic force component is provided to drive the short-stroke module. In both static and dynamic supports it is important that the support has very low stiffness to prevent the transmission of vibrations.
Previously, air-mounted bearings have been used to provide the static supports to support and isolate the metrology frame. While these systems do provide supports with very low stiffness, they have the disadvantage that they are relatively complicated, require a supply of compressed air (which in turn requires a compressor which produces vibrations that must be isolated from the lithographic apparatus) and are not suitable for use in a vacuum.
Previous solutions for both dynamic and static supports included the use of a pneumatic support to compensate for gravity. A pneumatic support is, for instance, disclosed in WO 99/05573 and EP 0973067 and may include a piston supported by a pressurized gas in a pressure chamber of a cylinder in which the piston is being journalled by a gas-bearing. The pneumatic support may require a rather large volume of pressurized gas to provide a good isolation from vibrations, and any turbulence and pressure variations in the pressurized gas will be transmitted to the piston and the supported object, which may make their application less effective and inconvenient. Prevention of transmission of vibrations in the support direction is quite successful but prevention of vibrations in a plane perpendicular to the support direction requires further measures such as a further gas-bearing allowing for frictionless movement in the perpendicular direction. Both a gas-bearing and a pneumatic support are not very well compatible with a vacuum environment.
Further, it has been proposed to provide a supporting force by a magnetic attraction and/or repulsion such as, for instance, disclosed in EP 1001512 or U.S. Pat. No. 5,780,943. However, the proposed solutions provide a supporting force that may be positional dependent both along and perpendicular to the support direction. The proposed solutions may also be subject to demagnetization effects.
It is an aspect of the present invention to provide supports which are relatively simple, suitable for use in a vacuum, require minimal services (such as compressed air and cooling) and provide substantially constant support within a defined operating volume, both along and perpendicular to the support direction.
It is yet another aspect of the invention to provide magnetic supports which take a small overall volume since space is generally very limited in lithographic apparatus where such magnetic supports may find their application.
Yet another aspect of the invention is to provide magnetic supports of which a nominal supporting force is easily adjustable.
Yet another object of the invention is to provide magnetic supports that may efficiently be combined with a current carrying element for providing an additional force along the support direction.
This and other aspects are achieved according to the invention in a lithographic apparatus including a radiation system constructed and arranged to supply a projection beam of radiation; a support structure for supporting a patterning device, the patterning device constructed and arranged to pattern the projection beam according to a desired pattern; a substrate table to hold a substrate; and a projection system constructed and arranged to project the patterned beam onto a target portion of the substrate; a support that provides a magnetic force in a first direction between a first part and a second part of the apparatus, wherein the support includes first, second and third magnet assemblies and the first and third magnet assemblies are attached to the first part and each includes at least one magnet oriented such that its magnetic polarization is substantially parallel or anti-parallel to the first direction; the first and third magnet assemblies define a space between them in a second direction that is substantially perpendicular to the first direction; the second magnet assembly is attached to the second part and includes at least one magnet, the second magnet assembly at least partly located in the space; and the at least one magnet of the second magnet assembly has its magnetic polarization oriented so as to produce a bias force substantially along the first direction by magnetic interaction between the first, second and third magnet assemblies.
Such a configuration of magnets provides a considerable volume in which the second magnet assembly can move without any substantial variation in the supporting force. This provides for a very low stiffness support both along and perpendicular to the support direction.
In an embodiment of the present invention at least one of the first, second and third magnet assemblies includes at least one permanent magnet. This is advantageous since electromagnets, in comparison, constantly require an electric current to provide the bias force. This in turn produces heat which must be dissipated and may necessitate additional cooling apparatus.
In another embodiment of the invention, the second magnet assembly circumscribes or encloses the first magnet assembly and the third magnet assembly circumscribes or encloses the second magnet assembly in a plane perpendicular to the first direction. Preferably at least one of the first, second and third magnet assemblies is annular in a cross-section perpendicular to the first direction. This is advantageous because variations in the magnet strength will have less effect on the characteristics of the magnetic support.
In a further embodiment of the present invention at least one of the first and third magnet assemblies includes two magnets which can be adjusted so as to vary their relative positions. This is advantageous as it allows the bias force to be altered depending on the load that the support is required to carry.
In a still further embodiment of the present invention a magnet of the third magnet assembly is oriented such that its magnetic polarization is substantially parallel to the magnetic polarization of a magnet of the first magnet assembly and a magnet of the second magnet assembly is oriented such that its magnetic polarization is substantially parallel or anti-parallel to that of a magnet of the first magnet assembly. This embodiment is advantageous as the resulting support may be relatively slender for a given size of bias force provided.
In a still further embodiment of the present invention a magnet of the third magnet assembly is oriented such that its magnetic polarization is substantially anti-parallel to that of a magnet of the first magnet assembly and a magnet of the second magnet assembly is oriented such that its magnetic polarization is substantially perpendicular to that of a magnet of the first magnet assembly. This embodiment is advantageous as it provides a support that has a relatively large travel within a given range of the maximum static force for a given size of the magnetic support.
In a still further embodiment of the invention, the support may further comprise an electrically conductive element, connectable to a power supply arranged so as to produce a force between the first and second parts of the apparatus by interaction between an electrical current carried by the electrically conductive element and a magnetic field of at least one of the first, second and third magnet assemblies. This is advantageous as the resulting force may be used to control the separation of the first and second parts of the lithographic apparatus.
In another aspect the invention provides for a lithographic apparatus including a radiation system constructed and arranged to supply a projection beam of radiation; a support structure constructed and arranged to support patterning device, the patterning device constructed and arranged to pattern the projection beam according to a desired pattern; a substrate table to hold a substrate; and a projection system constructed and arranged to project the patterned beam onto a target portion of the substrate; a support that provides a magnetic force in a first direction between a first part and a second part of the apparatus, wherein the support includes first, second and third magnet assemblies and the first and third magnet assemblies are attached to the first part and each includes at least one magnet oriented such that its magnetic polarization is substantially parallel or anti-parallel to the first direction, at least one of the first and third magnet assemblies having a substantially rotationally symmetric configuration around an axis along the first direction; the first and third magnet assemblies define a space between them; the second magnet assembly is attached to the second part and includes at least one magnet, the second magnet assembly at least partly being located in the space; and the at least one magnet of the second magnet assembly has its magnetic polarization oriented so as to produce a bias force substantially along the first direction by magnetic interaction between the first, second and third magnet assemblies.
In yet another aspect the invention provides for a lithographic apparatus including a radiation system constructed and arranged to supply a projection beam of radiation; a support structure constructed and arranged to support a patterning device, the patterning device constructed and arranged to pattern the projection beam according to a desired pattern; a substrate table to hold a substrate; and a projection system constructed and arranged to project the patterned beam onto a target portion of the substrate; a support that provides a magnetic force in a first direction between a first part and a second part of the apparatus, wherein the support includes first and second magnet assemblies and the second magnet assembly is attached to the second part and comprises at least one magnet having its magnetic polarization oriented so as to produce a bias force substantially along the first direction by magnetic interaction between the first and second magnet assemblies; and the first magnet assembly is attached to the first part and includes at least two permanent magnets, a relative position of the permanent magnets being adjustable so as to adjust the bias force.
In yet another aspect the invention provides for a lithographic apparatus including a radiation system constructed and arranged to supply a projection beam of radiation; a support structure constructed and arranged to support a patterning device, the patterning device constructed and arranged to pattern the projection beam according to a desired pattern; a substrate table to hold a substrate; and a projection system constructed and arranged to project the patterned beam onto a target portion of the substrate; a support that provides a magnetic force in a first direction between a first part and a second part of the apparatus, wherein the support includes first and second magnet assemblies and; the first magnet assembly is attached to the first part and has a magnetic polarization that is oriented substantially parallel or anti-parallel to the first direction; the second magnet assembly is attached to the second part and includes at least one magnet having its magnetic polarization oriented along a second direction perpendicular to the first direction so as to produce a bias force substantially along the first direction by magnetic interaction between the first and second magnet assemblies; and an electrically conductive element connectable to a power supply, the electrically conductive element being attached to the first part so as to produce a force parallel to the first direction between the first and second parts by interaction of an electrical current carried by the electrically conductive element and a magnetic field of the second magnet assembly.
According to yet a further aspect of the invention there is provided a device manufacturing method including providing a substrate that is at least partially covered by a layer of radiation-sensitive material; providing a projection beam of radiation using a radiation system; using a patterning device to endow the projection beam with a pattern in its cross-section; projecting the patterned beam of radiation onto a target portion of the layer of radiation-sensitive material; providing a support that provides a magnetic force in a first direction between a first part and a second part of the apparatus, comprising first, second and third magnet assemblies wherein the first and third magnet assemblies are attached to the first part and each comprises at least one magnet oriented such that its magnetic polarization is substantially parallel or anti-parallel to the first direction; the first and third magnet assemblies are arranged to define a space between them in a second direction that is substantially perpendicular to the first direction; the second magnet assembly is attached to the second part and comprises at least one magnet, the second magnet assembly at least partly located in the space; and the at least one magnet of the second magnet assembly has its magnetic polarization oriented so as to produce a bias force substantially along the support direction by magnetic interaction between the first, second and third magnet assemblies.
Although specific reference may be made in this text to the use of the apparatus according to the invention in the manufacture of ICs, it should be explicitly understood that such an apparatus has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. One of ordinary skill will appreciate that, in the context of such alternative applications, any use of the terms xe2x80x9creticlexe2x80x9d, xe2x80x9cwaferxe2x80x9d or xe2x80x9cdiexe2x80x9d in this text should be considered as being replaced by the more general terms xe2x80x9cmaskxe2x80x9d, xe2x80x9csubstratexe2x80x9d and xe2x80x9ctarget portionxe2x80x9d, respectively.
In the present document, the terms xe2x80x9cradiationxe2x80x9d and xe2x80x9cbeamxe2x80x9d are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation, (e.g. having a wavelength in the range 5-20 nm), as well as particle beams, such as ion beams or electron beams.